Add CollectionsMarshal.AsBytes(BitArray)

[stephentoub]

This entailed:

• Moving BitArray to corelib
• Inverting the endianness concerns so that the internal storage is always little endian
• Avoiding duplication of endianness-related changes by consolidating / deduplicating a bunch of the implementation (in particular around the SIMD implementations of And/Or/Xor/Not).
• As long as I was touching a bunch of the code, cleaning up some of the antiquated style aspects.

Still need to validate perf and likely fix some big endian issues.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-collections
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[stephentoub]

/azp list

[azure-pipelines]

CI/CD Pipelines for this repository:

• runtime-coreclr outerloop
• runtime-coreclr jitstress
• runtime-coreclr jitstressregs
• runtime-coreclr jitstress2-jitstressregs
• runtime-coreclr gcstress0x3-gcstress0xc
• runtime-coreclr gcstress-extra
• runtime-coreclr r2r-extra
• runtime-coreclr jitstress-isas-x86
• runtime-coreclr jitstress-isas-arm
• runtime-coreclr jitstressregs-x86
• runtime-coreclr libraries-jitstressregs
• runtime-coreclr libraries-jitstress2-jitstressregs
• runtime-coreclr r2r
• runtime-coreclr runincontext
• runtime-coreclr crossgen2
• runtime-libraries-coreclr outerloop
• runtime-libraries-coreclr outerloop-windows
• runtime-libraries-coreclr outerloop-linux
• runtime-libraries-coreclr outerloop-osx
• runtime
• runtime-libraries enterprise-linux
• runtime-libraries stress-http
• runtime-libraries stress-ssl
• runtime-dev-innerloop
• runtime-coreclr crossgen2 outerloop
• coreclr-release-outerloop-nightly
• runtime-coreclr crossgen2-composite
• runtime-jit-experimental
• runtime-coreclr libraries-jitstress
• dotnet-linker-tests
• runtime-coreclr ilasm
• runtime-coreclr crossgen2-composite gcstress
• runtime-coreclr pgo
• runtime-coreclr libraries-pgo
• Antigen
• runtime-community
• Fuzzlyn
• runtime-coreclr superpmi-replay
• runtime-wasm
• runtime-coreclr superpmi-diffs
• runtime-coreclr superpmi-asmdiffs-checked-release
• runtime-extra-platforms
• jit-cfg
• runtime-wasm-perf
• runtime-llvm
• runtime-coreclr jitstress-random
• runtime-coreclr libraries-jitstress-random
• runtime-android-grpc-client-tests
• runtime-wasm-non-libtests
• runtime-android
• runtime-androidemulator
• runtime-ioslike
• runtime-ioslikesimulator
• runtime-linuxbionic
• runtime-maccatalyst
• runtime-coreclr pgostress
• runtime-coreclr jitstress-isas-avx512
• runtime-libraries-mono outerloop
• runtime-sanitized
• runtime-wasm-dbgtests
• runtime-wasm-optional
• runtime-nativeaot-outerloop
• runtime-coreclr superpmi-collect-test
• runtime-diagnostics

[stephentoub]

/azp run runtime-community

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[stephentoub]

/azp run runtime-community

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[stephentoub]

/azp run runtime-community

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jkotas]

runtime-community

This does not run tests on big endian machines (disabled due to security). Replacement is being worked on, but it is not online yet.

I see that https://github.com/dotnet/runtime/blob/main/eng/pipelines/runtime-community.yml#L47 is a misleading comment - it does just a build, it does not run any tests. Could you please fix it while you are on it?